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> But CN is a "position finding" system, not a
> "position keeping" system so the accuracy of  
> a celestial fix is completely independent of prior
> fixes or DR errors

Agreed if you have multiple LOPs to work with - but in Earhart's case it's my 
understanding that Noonan was trying to locate the island based on only the 
one sun line (and we can assume, as you mention, that he deliberately 
navigated off-course one way or the other in order to know which way to turn 
when arriving at that LOP).

> Noonan would have known when he had his last fix 
> and would have allowed for DR uncertainty commensurate
> with the length of the DR leg.

So, at the risk of asking the obvious, why were they apparently unable to locate 
the island - even though they supposedly close to it (from what I've read, 
the Itasca reported that radio signals from the plane were loud and clear, 
and increasing in strength right up to her final transmission)?

--
GregR



--- On Wed, 1/13/10, Gary LaPook  wrote:

> From: Gary LaPook 
> Subject: [NavList] Re: Cessna CN Summary
> To: NavList@fer3.com
> Date: Wednesday, January 13, 2010, 2:56 PM
> 
> 
> 
>   
>   
> 
>  
> But CN is a "position finding" system, not a
> "position keeping" system
> so the accuracy of� a celestial fix is completely
> independent of prior
> fixes or DR errors. You can start� with three
> observations and know
> only that you are on the planet Earth and in only three
> iterations come
> up with a fix of normal accuracy. Noonan could have paddled
> a canoe
> across the Pacific to Howland and the final LOP used to
> find the island
> would be of normal accuracy. Dead reckoning ,� INS and
> Doppler� are
> "position keeping" systems so they acquire errors
> or uncertainty as
> time goes by. CN, GPS, LORAN, CONSOL, DECCA, VOR, visual
> bearings, and
> radio bearings are all� "position finding"
> systems. Interestingly,
> OMEGA has characteristics of both. OMEGA gives you an LOP
> within a
> "lane" but you must keep account of crossing the
> lanes to place the LOP
> within the correct lane. The normal way to do a single LOP
> landfall is
> to use the destination as the AP so if you want to plot the
> LOPs (which
> is not really necessary) then the LOPs get more accurate as
> you
> approach the island. The only impact of deterioration of
> the DR on a
> long leg is that one must aim off farther to the side to
> intercept the
> LOP through destination so that you can be certain on what
> side of the
> destination you intercept the LOP. Noonan would have known
> when he had
> his last fix and would have allowed for DR uncertainty
> commensurate
> with the length of the DR leg.
> 
> 
> 
> gl
> 
> 
> 
> 
> 
> 
> 
> Greg R. wrote:
> 
>   
>     a very experienced flight navigator, such as Fred
> Noonan, 
> should have been able to find anl island, such as Howland.
>     
>   
>   
> True enough - and while not wanting to disagree with your
> analysis, I'm not sure it's a valid comparison. 
> 
> Your flights had the benefit of a very recent and very
> close known position (i.e. Oxnard or Santa Paula airports,
> depending on where you departed from) that Earhart and
> Noonan didn't after 20-some hours over the open ocean. 
> 
> I would certainly hope that any halfway-decent navigator
> would be able to find an island (or at least an LOP through
> it) that's only a few tens of miles offshore with that
> as a starting point...  ;-)
> 
> --
> GregR
> 
> 
> 
> --- On Wed, 1/13/10, Gary LaPook 
> wrote:
> 
>   
>   
>     From: Gary LaPook 
> Subject: [NavList] Re: Cessna CN Summary
> To: NavList@fer3.com
> Date: Wednesday, January 13, 2010, 12:55 PM
> Even first timer flight navigators
> taking� sights achieved the accuracy needed to find an
> island. So,a very experienced flight navigator, such as
> Fred
> Noonan, should have been able to find anl island, such as
> Howland.
> 
> gl
> 
> gregrudzinski@yahoo.com
> wrote:
>     
>     
>       Three Flights Completed
> 
> Five Sun observations performed using a two minute
>       
>     
>     averager
>     
>     
>       ( Intercepts of 2A, 3A, 8A, 10A, 18A )
> 
> Six individual observations performed with four
>       
>     
>     consecutively averaged.
>     
>     
>       ( Average of four 9A, Individual from back seat
> 22T,
>       
>     
>     Individual from front seat 19T )
>     
>     
>       
> First Impression- The Bubble moves a great deal even
>       
>     
>     though the plane seems to be level and steady.
> This was most
> apparent when the horizon prism was flipped in on the MK 5
> where the bubble movement could be seen relative to the
> horizon. In spite of this reasonable accuracy was still
> obtained. Clearly there would have been no problem finding
> an island such as Anacapa (6NM long) with or without an
> averager but given the choice I would go with the averager.
>     
>     
>       Greg Rudzinski
> 
> 
> 
>       
>     
>    
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